In the flotation separation of minerals, reagents containing a sulfoxy radical, such as sodium sulfite, sodium bisulfite and sodium metabisulfite (or alkali metal or alkaline earth metal equivalents), sulfur dioxide or other thionates are used to improve the quality of the separation, particularly where sulfidic minerals such as chalcopyrite, pentlandite, pyrite, sphalerite, pyrrhotite or galena are present.
While such reagents are effective per se, unfortunately, the sulfoxy groups are susceptible to oxidation and, therefore, need to be continuously replenished during the mineral separation process to maintain their efficiency and thus the quality of the separation.
Oxidation may be caused by the presence of dissolved oxygen in water used within the mineral separation circuit which reacts with the sulfoxy compound to ultimately produce sulfate anions. Because such side reactions of dissolved oxygen and sulfoxy compounds result in consumption of sulfoxy compounds, increased dosage levels of sulfoxy compounds are required. Loss of sulfoxy reagents in this manner is endured by many flotation operations and may be a major cost, in some cases exceeding 25% of the milling costs.
Further, water present within the mineral separation circuit usually contains high levels of cations such as calcium and magnesium which can react with the sulfate anions. The result is a degree of side-reaction which creates significant quantities of precipitate or scale, typically gypsum, i.e. calcium sulfate. This scale builds up on the internal surfaces of processing equipment, notably pH control and level control probes and discharge sections. It goes without saying that such problems interfere with the effective control of the mineral separation process and extended maintenance periods are required for scale removal. Needless to say, both the loss of process control and excessive maintenance can have detrimental economic consequences.
Additionally, the supply of such sulfoxy compounds, generally as solids, to remotely located flotation plant sites, as well as storage and preparation for use result in costs which have significant effects on the economics and productivity of such sites. Hence, it will be appreciated that these costs can be minimized by the more efficient use of sulfoxy radical-containing reagents in the process. In this manner, the present invention seeks to overcome at least some of the problems of the prior art or at least provide a commercial alternative to prior art techniques.